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CVE-2026-59887— linkify-it: Quadratic-complexity DoS via the `mailto:` validator scan-loop on attacker text

Quick assessment

Affected
markdown-it linkify-it
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Markdown it! linkify-it是Markdown it!组织开源的一款协议解析与链接识别工具。 Markdown it! linkify-it 5.0.2之前版本存在资源管理错误漏洞，该漏洞源于mailto: schema验证器在每次出现mailto:时被调用，并通过src_email_name扫描剩余输入，导致用户构造的文本CPU消耗呈O(n²)。

CVSS 7.5 · High EPSS 0.64% · P50

Possible ATT&CK Techniques 1 AI

T1496 · Resource Hijacking

Affected Version Matrix 1

VendorProduct Version RangeStatus
markdown-it linkify-it < 5.0.2 affected
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I. Basic Information for CVE-2026-59887

Vulnerability Information
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Vulnerability Title
linkify-it: Quadratic-complexity DoS via the `mailto:` validator scan-loop on attacker text
Source: CVE Program / CVE List V5
Vulnerability Description
linkify-it is a links recognition library with full Unicode support. Prior to 5.0.2, the mailto: schema validator used by .test() and .match() can be invoked at every mailto: occurrence and scan the remaining input through src_email_name in lib/re.mjs, causing O(n^2) CPU consumption on crafted user text. This issue is fixed in version 5.0.2.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
算法复杂性
Source: CVE Program / CVE List V5
Vulnerability Title
Markdown it! linkify-it 资源管理错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Markdown it! linkify-it是Markdown it!组织开源的一款协议解析与链接识别工具。 Markdown it! linkify-it 5.0.2之前版本存在资源管理错误漏洞，该漏洞源于mailto: schema验证器在每次出现mailto:时被调用，并通过src_email_name扫描剩余输入，导致用户构造的文本CPU消耗呈O(n²)。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
markdown-it linkify-it < 5.0.2 -

II. Public POCs for CVE-2026-59887

# POC Description Source Link Shenlong Link
AI-Generated POC Premium
Qwen3.6-35B-A3B · 122524 chars
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III. Intelligence Information for CVE-2026-59887

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Patches & Fixes for CVE-2026-59887 (1)

Vendor Advisories for CVE-2026-59887 (1)

Vendor Pages for CVE-2026-59887 (1)

IV. Related Vulnerabilities

Same product: linkify-it
Same vendor: markdown-it
Same weakness: CWE-407

V. Comments for CVE-2026-59887

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